using System.Globalization;
using Microsoft.Data.SqlClient;
using Microsoft.EntityFrameworkCore;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Configuration;

namespace ZB.MOM.WW.OtOpcUa.AdminUI.Tests;

/// <summary>
///     A real SQL Server database for the handful of AdminUI tests whose subject is the SQL Server
///     provider's LINQ <b>translation</b> rather than the C# around it — EF InMemory evaluates those
///     queries in-process, so it can neither fail on an untranslatable shape nor reproduce SQL Server's
///     collation semantics. Creates a uniquely-named database, applies the EF migrations to it, and drops
///     it at collection teardown.
/// </summary>
/// <remarks>
///     <para>
///         Shaped after <c>ZB.MOM.WW.OtOpcUa.Configuration.Tests.SchemaComplianceFixture</c> (same env
///         vars, same unique-name + <c>Migrate()</c> + drop-via-master lifecycle) with <b>one deliberate
///         deviation</b>: that fixture lets the connection failure surface as a constructor throw, so
///         Configuration.Tests fails hard when SQL Server is unreachable. AdminUI.Tests is an ordinary
///         unit suite that must stay green offline, so this fixture probes reachability FIRST and records
///         a <see cref="SkipReason"/> instead of throwing. Tests carry <see cref="SqlServerFactAttribute"/>,
///         which skips them when the probe failed.
///     </para>
///     <para>
///         The skip is an attribute rather than the <c>Assert.Skip(fixture.SkipReason)</c> call the S7
///         integration suite uses, because AdminUI.Tests is one of the three projects pinned to
///         <b>xunit v2</b> by <c>Akka.TestKit.Xunit2</c> (see <c>Directory.Packages.props</c>) and
///         <c>Assert.Skip</c> is xunit v3 only. Overriding <c>FactAttribute.Skip</c> is the v2 equivalent
///         and reports a genuine "skipped", not a vacuous pass. Both the attribute and this fixture read
///         the same one-shot probe in <see cref="AdminUiSqlServer"/>, so a session probes once.
///     </para>
///     <para>
///         The probe being <b>one-shot</b> bounds what "stays green offline" guarantees: it covers SQL
///         being unreachable <i>before the run</i>. A connectivity blip <i>during</i> a run is never
///         re-probed, so the affected tests surface as <c>SqlException</c> <b>failures</b>, not skips.
///     </para>
///     <para>
///         Every test in the collection shares ONE database (migrating is the expensive part), so tests
///         must isolate themselves by seeding uniquely-named rows, or by clearing the table they measure.
///         xunit serialises a collection's tests, so a clear-then-seed is safe.
///     </para>
/// </remarks>
public sealed class AdminUiSqlServerFixture : IDisposable
{
    /// <summary>Gets the name of the per-run test database, or <see langword="null"/> when SQL is unreachable.</summary>
    public string? DatabaseName { get; }

    /// <summary>Gets the connection string for the test database, or <see langword="null"/> when SQL is unreachable.</summary>
    public string? ConnectionString { get; }

    /// <summary>
    ///     Gets the reason the SQL-backed tests cannot run (server unreachable, migration failed), or
    ///     <see langword="null"/> when the database is ready.
    /// </summary>
    public string? SkipReason { get; }

    /// <summary>
    ///     Gets a context factory pointed at the migrated test database — the seam the services under test
    ///     (<c>DeploymentDriftProbe</c>, <c>RawTreeService</c>) take. Throws when <see cref="SkipReason"/>
    ///     is set; guard with <see cref="SqlServerFactAttribute"/>.
    /// </summary>
    public IDbContextFactory<OtOpcUaConfigDbContext> Factory =>
        _factory ?? throw new InvalidOperationException(SkipReason ?? "SQL Server fixture is not available.");

    private readonly SqlServerContextFactory? _factory;

    /// <summary>Initializes a new instance of the <see cref="AdminUiSqlServerFixture"/> class.</summary>
    public AdminUiSqlServerFixture()
    {
        // Probe FIRST — see the remarks. A dead server must leave this constructor without throwing,
        // because xunit builds collection fixtures before it discovers that every test is skipped.
        SkipReason = AdminUiSqlServer.SkipReason;
        if (SkipReason is not null) return;

        // A killed test process never reaches Dispose, so its database outlives the run. Reap the ones
        // old enough to be certainly nobody's (once per process, and only after the probe answered).
        AdminUiSqlServer.ReapOrphanedTestDatabasesOnce();

        // Mint from the same constant the reaper's LIKE anchors on — a rename that touched only one of the
        // two would leave every future database unreapable, with nothing to signal it.
        DatabaseName =
            $"{AdminUiSqlServer.TestDatabasePrefix}{DateTime.UtcNow:yyyyMMddHHmmss}_{Guid.NewGuid():N}";
        ConnectionString = AdminUiSqlServer.ConnectionStringFor(DatabaseName);

        try
        {
            var options = new DbContextOptionsBuilder<OtOpcUaConfigDbContext>()
                .UseSqlServer(ConnectionString)
                .Options;

            using var ctx = new OtOpcUaConfigDbContext(options);
            ctx.Database.Migrate();
        }
        catch (Exception ex)
        {
            // A half-created database would leak, so tear it down before standing the suite down.
            TryDropDatabase();
            SkipReason = $"Could not migrate the AdminUI SQL test database: {ex.Message}";
            DatabaseName = null;
            ConnectionString = null;
            return;
        }

        _factory = new SqlServerContextFactory(ConnectionString);
    }

    /// <summary>Disposes the fixture, dropping the test database.</summary>
    public void Dispose() => TryDropDatabase();

    private void TryDropDatabase()
    {
        if (ConnectionString is null || DatabaseName is null) return;

        var master = new SqlConnectionStringBuilder(ConnectionString) { InitialCatalog = "master" }.ConnectionString;
        SqlTestDatabaseReaper.TryDropDatabase(master, DatabaseName);
    }

    private sealed class SqlServerContextFactory(string connectionString)
        : IDbContextFactory<OtOpcUaConfigDbContext>
    {
        public OtOpcUaConfigDbContext CreateDbContext() =>
            new(new DbContextOptionsBuilder<OtOpcUaConfigDbContext>()
                .UseSqlServer(connectionString)
                .Options);

        public Task<OtOpcUaConfigDbContext> CreateDbContextAsync(CancellationToken cancellationToken = default) =>
            Task.FromResult(CreateDbContext());
    }
}

/// <summary>
///     One-shot reachability probe + connection-string builder shared by
///     <see cref="AdminUiSqlServerFixture"/> and <see cref="SqlServerFactAttribute"/>. The attribute is
///     constructed at discovery time and the fixture at collection start, so the probe must be cached or
///     a run pays the connect timeout twice.
/// </summary>
internal static class AdminUiSqlServer
{
    /// <summary>The name prefix every AdminUI test database carries; also the reaper's LIKE anchor.</summary>
    public const string TestDatabasePrefix = "OtOpcUaAdminUi_Test_";

    private const string DefaultServer = "10.100.0.35,14330";
    private const string DefaultSaPassword = "OtOpcUaDev_2026!";
    private const int ProbeTimeoutSeconds = 3;

    /// <summary>How long a test database must have existed before the reaper considers it certainly orphaned.</summary>
    private static readonly TimeSpan OrphanAge = TimeSpan.FromHours(24);

    private static readonly Lazy<string?> Probe = new(RunProbe, LazyThreadSafetyMode.ExecutionAndPublication);

    private static readonly Lazy<int> Reaper = new(RunReaper, LazyThreadSafetyMode.ExecutionAndPublication);

    /// <summary>Gets the reason SQL Server is unusable, or <see langword="null"/> when it answered.</summary>
    public static string? SkipReason => Probe.Value;

    /// <summary>
    ///     Reaps orphaned AdminUI test databases older than 24 hours, at most once per process. Call only
    ///     after <see cref="SkipReason"/> came back <see langword="null"/> — the reaper never throws, but
    ///     against a dead server it would just burn a connect timeout for nothing.
    /// </summary>
    public static void ReapOrphanedTestDatabasesOnce() => _ = Reaper.Value;

    /// <summary>Builds a connection string for the named database on the configured test server.</summary>
    /// <param name="database">The database to connect to.</param>
    /// <returns>The connection string.</returns>
    public static string ConnectionStringFor(string database)
    {
        var server = Environment.GetEnvironmentVariable("OTOPCUA_CONFIG_TEST_SERVER") ?? DefaultServer;
        var password = Environment.GetEnvironmentVariable("OTOPCUA_CONFIG_TEST_SA_PASSWORD") ?? DefaultSaPassword;

        return $"Server={server};Database={database};User Id=sa;Password={password};" +
               "TrustServerCertificate=True;Encrypt=False;";
    }

    private static int RunReaper() =>
        SqlTestDatabaseReaper.ReapOrphans(
            ConnectionStringFor("master"),
            TestDatabasePrefix,
            DateTime.UtcNow - OrphanAge).Count;

    private static string? RunProbe()
    {
        var server = Environment.GetEnvironmentVariable("OTOPCUA_CONFIG_TEST_SERVER") ?? DefaultServer;

        try
        {
            var probe = new SqlConnectionStringBuilder(ConnectionStringFor("master"))
            {
                ConnectTimeout = ProbeTimeoutSeconds,
            }.ConnectionString;

            using var conn = new SqlConnection(probe);
            conn.Open();
            return null;
        }
        catch (Exception ex)
        {
            return $"SQL Server at '{server}' is unreachable ({ex.GetType().Name}: {ex.Message}); " +
                   "set OTOPCUA_CONFIG_TEST_SERVER / OTOPCUA_CONFIG_TEST_SA_PASSWORD to point at a reachable instance.";
        }
    }
}

/// <summary>
///     Drops test databases that a killed test process left behind on the <b>shared</b> SQL Server.
/// </summary>
/// <remarks>
///     <para>
///         Every fixture here names its database <c>{prefix}{yyyyMMddHHmmss-UTC}_{guid:N}</c> and drops it
///         in <c>Dispose</c> — which a <c>Ctrl-C</c>, a crashed runner or a killed container never reaches,
///         so the database survives forever on an instance nobody gardens.
///     </para>
///     <para>
///         This is <c>DROP DATABASE</c> against a server other people share, so the rules are deliberately
///         narrow and every one of them is load-bearing:
///     </para>
///     <list type="bullet">
///         <item>
///             the <c>LIKE</c> is an <b>exact prefix</b> with <c>_</c> escaped (an unescaped <c>_</c> is a
///             single-character wildcard in T-SQL) — never widen it;
///         </item>
///         <item>
///             a matching name is dropped only when its <b>whole</b> shape is one this code could have
///             minted — prefix, a parseable 14-digit UTC timestamp, <c>_</c>, then 32 hex digits. That is
///             belt <i>and</i> braces against second-order injection: the name is also passed as a
///             <b>parameter</b> through <c>QUOTENAME</c> rather than interpolated into DDL, but the shape
///             check independently guarantees a candidate cannot contain <c>]</c> or <c>'</c>;
///         </item>
///         <item>
///             only names <b>strictly older than the cutoff</b> are dropped. At 24 hours that is far beyond
///             any run, so the reaper can never race a live sibling run on the same server; and
///         </item>
///         <item>
///             nothing here ever throws. A reaper that fails a green run would be worse than the leak it
///             cleans up.
///         </item>
///     </list>
/// </remarks>
internal static class SqlTestDatabaseReaper
{
    private const string TimestampFormat = "yyyyMMddHHmmss";
    private const int ConnectTimeoutSeconds = 3;

    /// <summary>
    ///     Drops every database matching <paramref name="prefix"/> whose embedded creation timestamp is
    ///     strictly older than <paramref name="cutoffUtc"/>.
    /// </summary>
    /// <param name="masterConnectionString">A connection string pointed at <c>master</c>.</param>
    /// <param name="prefix">The exact test-database name prefix, e.g. <c>OtOpcUaAdminUi_Test_</c>.</param>
    /// <param name="cutoffUtc">Databases created strictly before this UTC instant are dropped.</param>
    /// <returns>The names actually dropped; empty when there was nothing to reap or anything went wrong.</returns>
    internal static IReadOnlyList<string> ReapOrphans(string masterConnectionString, string prefix, DateTime cutoffUtc)
    {
        var reaped = new List<string>();

        try
        {
            foreach (var name in ListCandidates(masterConnectionString, prefix))
            {
                if (!TryParseCreatedUtc(name, prefix, out var createdUtc)) continue;
                if (createdUtc >= cutoffUtc) continue;

                try
                {
                    if (TryDropDatabase(masterConnectionString, name)) reaped.Add(name);
                }
                catch (Exception)
                {
                    // One stubborn database must not stop the sweep, nor fail the run that triggered it.
                }
            }
        }
        catch (Exception)
        {
            // Enumeration failed (server down, no permission). Reaping is opportunistic housekeeping.
        }

        if (reaped.Count > 0)
        {
            Console.WriteLine(
                $"[sql-test-reaper] dropped {reaped.Count} orphaned test database(s) older than " +
                $"{cutoffUtc:yyyy-MM-dd HH:mm:ss}Z: {string.Join(", ", reaped)}");
        }

        return reaped;
    }

    /// <summary>
    ///     Drops the named database, swallowing every failure — this is called unwrapped from
    ///     <c>Dispose</c> and from test <c>finally</c> blocks, so it must be genuinely best-effort.
    /// </summary>
    /// <remarks>
    ///     The database name is an <b>identifier</b>, which cannot be parameterised directly, so it rides
    ///     in as a parameter and <c>QUOTENAME</c> escapes it server-side. Interpolating it into the DDL
    ///     instead would make any attacker-chosen database name on this shared server a second-order
    ///     injection executed as <c>sa</c>.
    /// </remarks>
    /// <param name="masterConnectionString">A connection string pointed at <c>master</c>.</param>
    /// <param name="databaseName">The database to drop.</param>
    /// <returns><see langword="true"/> when the statement ran without error.</returns>
    internal static bool TryDropDatabase(string masterConnectionString, string databaseName)
    {
        try
        {
            using var conn = new SqlConnection(masterConnectionString);
            conn.Open();

            using var cmd = conn.CreateCommand();

            // The QUOTENAME result must be assembled into a variable first: EXEC(<string>) accepts only a
            // concatenation of literals and variables, so the tempting one-liner
            // EXEC('ALTER DATABASE ' + QUOTENAME(@name) + …) is a syntax error, not a subtle bug.
            cmd.CommandText = @"
DECLARE @sql nvarchar(max);
IF DB_ID(@name) IS NOT NULL
BEGIN
    SET @sql = N'ALTER DATABASE ' + QUOTENAME(@name) + N' SET SINGLE_USER WITH ROLLBACK IMMEDIATE; ' +
               N'DROP DATABASE ' + QUOTENAME(@name) + N';';
    EXEC sp_executesql @sql;
END";
            cmd.Parameters.Add(new SqlParameter("@name", databaseName));

            cmd.ExecuteNonQuery();
            return true;
        }
        catch (Exception)
        {
            // Teardown is best-effort: a dropped connection here must not fail an otherwise-green run.
            // The database name carries a timestamp, so a leaked one is reaped by the next run instead.
            return false;
        }
    }

    private static List<string> ListCandidates(string masterConnectionString, string prefix)
    {
        var names = new List<string>();

        // A short connect timeout, because this runs BEFORE whatever the fixture does next: on an
        // unreachable server the default ~15 s would simply be added to the latency the caller already pays.
        var probe = new SqlConnectionStringBuilder(masterConnectionString)
        {
            ConnectTimeout = ConnectTimeoutSeconds,
        }.ConnectionString;

        using var conn = new SqlConnection(probe);
        conn.Open();

        using var cmd = conn.CreateCommand();
        cmd.CommandText = @"SELECT name FROM sys.databases WHERE name LIKE @pattern ESCAPE '\'";
        cmd.Parameters.Add(new SqlParameter("@pattern", prefix.Replace("_", @"\_", StringComparison.Ordinal) + "%"));

        using var reader = cmd.ExecuteReader();
        while (reader.Read()) names.Add(reader.GetString(0));

        return names;
    }

    private static bool TryParseCreatedUtc(string databaseName, string prefix, out DateTime createdUtc)
    {
        createdUtc = default;

        if (!databaseName.StartsWith(prefix, StringComparison.Ordinal)) return false;

        var rest = databaseName.AsSpan(prefix.Length);

        // Expect exactly "<14-digit timestamp>_<32 hex digits>" — anything else is not a name this code
        // minted. Validating the GUID tail is what bounds the character set of every candidate name: a
        // "N"-format GUID is hex only, so no candidate can carry a ']' or a quote into the drop statement.
        if (rest.Length < TimestampFormat.Length + 1 || rest[TimestampFormat.Length] != '_') return false;
        if (!Guid.TryParseExact(rest[(TimestampFormat.Length + 1)..], "N", out _)) return false;

        return DateTime.TryParseExact(
            rest[..TimestampFormat.Length],
            TimestampFormat,
            CultureInfo.InvariantCulture,
            DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal,
            out createdUtc);
    }
}

/// <summary>
///     A <see cref="FactAttribute"/> that skips itself when the shared test SQL Server is unreachable.
///     The xunit v2 equivalent of xunit v3's <c>Assert.Skip</c> — see
///     <see cref="AdminUiSqlServerFixture"/>'s remarks for why this project cannot use the latter.
/// </summary>
[AttributeUsage(AttributeTargets.Method)]
public sealed class SqlServerFactAttribute : FactAttribute
{
    /// <summary>Initializes a new instance of the <see cref="SqlServerFactAttribute"/> class.</summary>
    public SqlServerFactAttribute()
    {
        if (AdminUiSqlServer.SkipReason is { } reason) Skip = reason;
    }
}

/// <summary>Collection definition binding the SQL-backed AdminUI tests to one shared database.</summary>
[CollectionDefinition(nameof(AdminUiSqlServerCollection))]
public sealed class AdminUiSqlServerCollection : ICollectionFixture<AdminUiSqlServerFixture>
{
}